We will continue our work on the generation of lines as assay systems for antigen presentation to determine Ia's role in recognition of antigen by T lymphocytes. We will further examine the role of Ia molecules in skin graft rejection in I region compatable strains. We will also examine the role of Ia in non lymphoid tissue such as brain and the potential for an endogeneous lymphoid immune system in the brain. Further we will begin studies on genetic organization at the molecular level of chromosome 17 DNA sequences in collaboration with other laboratories.